Figure 2. γ-secretase inhibitors enhance radiation-induced cell death in glioma stem cells.

(A) T4302 CD133+ cells were pre-treated with DAPT or L685,458 for 4 hours, and irradiated at 3 Gy. Percentage of dead cells was determined by trypan blue exclusion assay at 48 hours after radiation exposure. (B) T4302 CD133+ cells were treated with GSIs ± radiation as indicated. Cells were then plated at 3000 cells per well in 96-well plates. Relative caspase 3/7 activities were determined by normalizing caspase activities to the corresponding cell titers. (C, D) Relative caspase 3/7 activities of T3359 and T3691 CD133+ cells at 72 hours after radiation were determined as described above. (E) T4302 CD133+ cells were treated as described in figure 2A. 24 or 48 hours after radiation exposure, cells were labeled with FITC-conjugated Annexin V antibody (BD Sciences) according to manufacturer’s instructions and analyzed by flow cytometry. (F) T4302 CD133+ cells were pre-treated with 2 μM DAPT for 4 hours, and were left unirradiated or irradiated at 1, 2 or 3 Gy. Relative caspase 3/7 activities were determined at 72 hours after radiation. (G) T4302 CD133+ cells were pre-treated with DAPT at indicated concentrations for 4 hours, and irradiated at 3 Gy. Relative caspase activities were determined at 48 or 72 hours after radiation.